Besides some smaller changes and bug-fixes, the new release is mainly exciting for classical music enthusiasts. In October, iTunes introduced new tag fields for better tagging of classical music. Those fields include work name, movement name, number and total count and are now mapped in Mp3tag to these new field names:

While the implementation of these fields in iTunes is not yet realized completely consistent, Mp3tag supports all fields for MP4 tags. For MP3 files, iTunes currently writes the work name to the CONTENTGROUP field (while what's added at "Grouping" is only stored in iTunes' internal database). The same applies to the flag SHOWMOVEMENT, which is also stored in iTunes' internal database and not in the file itself. There are already several bug reports for that reported to Apple and I expect a consistent implementation with the next release of iTunes.

While the implementation of these fields in iTunes is not yet realized completely consistent, Mp3tag supports all fields for MP4 tags. For MP3 files, iTunes currently writes the work name to the CONTENTGROUP field (while what's added at "Grouping" is only stored in iTunes' internal database). The same applies to the flag SHOWMOVEMENT, which is also stored in iTunes' internal database and not in the file itself. There are already several bug reports for that reported to Apple and I expect a consistent implementation with the next release of iTunes.

Thanks Florian,

Unfortunately this still hasn't been solved in iTunes 12.5.4.

This Bug seems to be the cause that keeps my iPhone syncing some songs over and over again. It only stopped doing this after I removed the "work name" from within iTunes.

I also have been plagued with the repeated syncing of all songs in the iTunes library due to trying to use "Work" instead of "Grouping" in smart playlists, which is still very buggy (appears to be working in iTunes, but is ignored on the playlists on IOS devices). However, more developments from iTunes' latest release 12.5.4.42 yesterday: Evidently iTunes is now writing "Grouping" values from its library out to a new ID3 frame "GRP1". This could be promising news for those of us who were using the problematic "Work" / TIT1 frame to store mood & style keywords and instead park them in the new "GRP1" frame and import them back into iTunes' Grouping field and go back to referencing "Grouping" instead of "Work". If only some real awesome 3rd party tagger supported the new GRP1 (iTunes Grouping) frame... hint hint

Has something happened to rg2sc?
I've just noticed this over the past week after updating to the latest 2.80 version. The $rg2sc function doesn't appear to be writing anything out to the ITUNNORM tag. I invoke it using the action that garym kindly posted here.

Looking back through my collection, I suspect the problem began with the 2.79 upgrade, but I've only just noticed it in the past couple of days.

[Edit]
I did some experiments and found the problem isn't with the $rg2sc function, which works fine when called directly. Instead, something's changed with the control logic for action scripts. garym's combined action uses simple logic on the file extension to detemine how to tag the soundcheck info, and this now seems to be failing, whereas it worked fine before:

Interesting, looks like frames "TIT1" (CONTENTGROUP) and "TCON" (GENRE) got switched around. I tried the same test, but it didn't rewrite the file out after playing it, and I have both frames populated.

On my PC, If CONTENTGROUP is NOT BLANK, Format is MP3 and iTunes plays the song it changes the files. Did a test last night and 8 songs (out of 40) got changed.

Previously in these files the "WORK" was EMPTY, but after playing and iTunes changing the files "WORK" was populated with CONTENTGROUP and this caused my iDevices to resync these (8) files over and over again.

I found with the Mp3tag filter mechanism and these filters

%_tag% IS "ID3v1 ID3v2.3" AND NOT %contentgroup% IS ""
%_tag% IS "ID3v2.3" AND NOT %contentgroup% IS ""

That I have to change around 3000 Songs to prevent iTunes changing the files, but I have decided to wait (and not play songs with iTunes anymore) till either iTunes fixes it or Mp3tag supports the change you proposed and hopefully that solves it.

[...]In October, iTunes introduced new tag fields for better tagging of classical music. Those fields include work name, movement name, number and total count and are now mapped in Mp3tag to these new field names:
[list]
[]MOVEMENTNAME — Movement name
[]MOVEMENT — Movement number
[]MOVEMENTTOTAL — Movement count
[]WORK — Work name
[*]SHOWMOVEMENT — Flag to trigger showing of classical fields instead of normal title in iTunes (1 = yes)[...]